Silicon-based film and photovoltaic element

ABSTRACT

A silicon-based film is provided which comprises a crystal phase formed on a substrate with a surface shape represented by a function f, wherein the silicon-based film is formed on a substrate with a surface shape having a standard deviation of an inclination arctan (df/dx) from 15° to 55° within the range of a sampling length dx from 20 nm to 100 nm, a Raman scattering strength resulting from an amorphous component in the silicon-based film is not more than a Raman scattering strength resulting from a crystalline component, and a difference between a spacing in a direction parallel to a principal surface of the substrate and a spacing of single crystal silicon is within the range of 0.2% to 1.0% with regard to the spacing of the single crystal silicon.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a silicon-based film and aphotovoltaic element comprising a silicon-based semiconductor layer withat least one pin junction on a support, such as a solar cell, a sensorand the like.

[0003] 2. Related Background Art

[0004] As a method of forming a silicon-based film showingcrystallinity, some methods like the cast method in which the film isgrown in a liquid phase have been conventionally carried out, but thesemethods need high temperature processing and have some problems inachieving mass production and low-cost production.

[0005] As a method of forming a silicon-based film showing crystallinityother than the cast method, some methods are disclosed which include amethod described in Japanese Patent Application Laid-Open No. 5-109638in which a polycrystalline silicon film is formed by growing anamorphous silicon film in a solid phase and a method described inJapanese Patent Application Laid-Open No. 5-136062 in which afteramorphous silicon film has been formed, a hydrogen plasma processing iscarried out, and a polycrystalline silicon film is formed by repeatingthe procedure.

[0006] However, in these already disclosed methods of forming asilicon-based film showing crystallinity, the former method had aproblem that a heat treatment for a long time was needed to crystallizea semiconductor layer with a thickness of several μm or more using asolid phase reaction, and the latter method had a problem that theprocessing time was increased due to repeating the hydrogen plasmaprocessing and the formation of a silicon film.

[0007] Furthermore, when a substrate having an uneven surface shape wasadopted as a means of increasing the optical confinement effect, in asilicon-based film showing an orientation property, especially in asilicon-based film having a columnar structure in the thicknessdirection, the growth of an orientation plane in the tangentialdirection of the unevenness in the early stage of the film formation wasa cause for generating irregular crystal boundaries in the growingprocess.

SUMMARY OF THE INVENTION

[0008] Accordingly, an object of the present invention is to provide asilicon-based film that can settle the above described problems, canform a film at a low cost and at a high film forming rate that attains aprocessing time of an industrially acceptable level, and shows excellentcharacteristics, especially on a substrate having an uneven surfaceshape, and to provide a photovoltaic element that has such asilicon-based film and is excellent in photoelectric characteristics.

[0009] The silicon-based film of the present invention comprises acrystal phase formed on a substrate with a surface shape represented bya function f, wherein the silicon-based film is formed on a substratewith a surface shape having a standard deviation of an inclinationarctan (df/dx) from 15° to 55° within the range of a sampling length dxfrom 20 nm to 100 nm, a Raman scattering strength resulting from anamorphous component in the silicon-based film is not more than a Ramanscattering strength resulting from a crystalline component, and adifference between a spacing in a direction parallel to a principalsurface of the substrate and a spacing of single crystal silicon iswithin the range of 0.2% to 1.0% with regard to the spacing of thesingle crystal silicon.

[0010] Further, the present invention provides a silicon-based film thatis characterized in that the above described silicon-based filmcomprising a crystal phase comprises a crystal of a columnar structurein the thickness direction.

[0011] Furthermore, the present invention provides a silicon-based filmthat is characterized in that the percentage of diffraction strength of(220) plane according to X-ray or electron beam diffraction is 30% ormore of the total diffraction strength.

[0012] Moreover, the present invention provides a photovoltaic elementthat is characterized in that in a photovoltaic element comprising asilicon-based semiconductor layer having at least one pin junction on asupport, at least one i-type semiconductor layer comprises the abovedescribed silicon-based film.

[0013] In addition, the present invention provides a photovoltaicelement that is characterized in that the above described silicon-basedsemiconductor layer is formed on a substrate comprising at least a firsttransparent conductive layer stacked on a support, the first transparentconductive layer has the above described surface shape.

[0014] Further, the present invention provides a photovoltaic elementthat is characterized in that the above described silicon-based film isprepared by a plasma CVD method using a high frequency.

[0015] The frequency of the above described high frequency is preferableto be 10 MHz or more and be 10 GHz or less. The above described supportis preferable to be a conductive support.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a schematic sectional view showing one example of aphotovoltaic element of the present invention;

[0017]FIG. 2 is a schematic sectional view showing one example of adeposited film forming apparatus to produce a silicon-based film and aphotovoltaic element of the present invention;

[0018]FIG. 3 is a schematic sectional view showing one example of adeposited film forming apparatus to produce a silicon-based film and aphotovoltaic element of the present invention;

[0019]FIG. 4 is a schematic sectional view showing one example of aphotovoltaic element comprising a silicon-based film of the presentinvention;

[0020]FIG. 5 is a schematic sectional view showing one example of aphotovoltaic element comprising a silicon-based film of the presentinvention;

[0021]FIG. 6 is a conceptual diagram of measuring the distribution ofinclinations; and

[0022]FIG. 7 is a schematic view of subcells.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The present inventor has eagerly conducted studies repeatedly tosolve the above described problems and has resulted in finding that in asilicon-based film comprising a crystal phase formed on a substrate, theabove described silicon-based film is formed on a substrate in which thestandard deviation of the inclination arctan (df/dx) is from 15° to 55°in the range where the sampling length dx of the cross-sectional shape fof the surface is from 20 nm to 100 nm, that a silicon-based film inwhich a Raman scattering strength resulting from an amorphous componentin the above described silicon-based film is not more than a Ramanscattering strength resulting from a crystalline component, and thedifference between the spacing in the direction parallel to theprincipal surface of the above described substrate (a macroscopic andvirtual substrate surface obtained by ignoring the unevenness of thesurface) and the spacing of single crystal silicon is within the rangeof 0.2% to 1.0% to the spacing of single crystal silicon is possible toform a silicon film comprising a crystal phase with a low defect densityand good quality even if it has an uneven surface shape, and that in aphotovoltaic element formed with the use of the silicon-base film,because good photoelectric conversion characteristics can be obtained, afactor of generating cracks in the film is suppressed, the formedsurface is cleansed and others, the photovoltaic element is improved inits adhesion with the substrate and shows good environmental resistance.

[0024] The following actions can be obtained by making the abovedescribed constitution.

[0025] A method of forming a silicon-based semiconductor film comprisinga crystal phase by the plasma CVD method using a high frequency isadvantageous in achieving low-cost production as compared to a solidphase reaction because the process time can be shortened and the processtemperature can also be lowered. In particular, in a photovoltaicelement having a pin junction, this effect is greatly exhibited byapplying it to an i-type semiconductor layer with a greater filmthickness.

[0026] When an i-type semiconductor layer substantially functioning as alight absorbing layer is an i-type semiconductor layer comprising acrystal phase, there is such an merit that a photodegradation phenomenondue to the Staebler-Wronski effect, which becomes a problem in case ofan amorphous material, can be restrained. The present inventor haseagerly conducted studies repeatedly and has resulted in finding thatthe above described effect appears more remarkably in an i-typesemiconductor layer formed so that a Raman scattering strength resultingfrom an amorphous component (a typical example is in the vicinity of 480cm⁻¹) is not more than a Raman scattering strength resulting from acrystalline component (a typical example is in the vicinity of 520cm⁻¹).

[0027] Here, as a point at issue in an i-type semiconductor layercomprising a crystal phase, it is known that grain boundaries haveinfluences on both major carriers and minority carriers to deterioratetheir performance. In order to restrain the influences of grainboundaries, it is considered to be one of effective means to lower thecrystal grain boundary density by making the crystal grain size in ani-type semiconductor layer larger.

[0028] Further, when carrier travel in the thickness direction, aconstitution in which columnar crystal grains are arranged in thethickness direction is more preferable than a constitution in whichcrystal grains are randomly arranged because it is possible to lower thefrequency of carriers to cross grain boundaries. In particular, whencolumnar crystal grains are selectively oriented on (220) plane, thesurface is considered to function as an i-type semiconductor layer inwhich the mobility of the carrier is more excellent, because the crystalgrains have the channel structure of a hexagon form in the directionperpendicular to the substrate surface and the like. As is clearly seenfrom ASTM cards, the percentage of the diffraction strength in the (220)plane to the total amount of diffraction strength of 11 reflection partsfrom a low angle side is about 23% in non-orientating crystallinesilicon. That is, it means that a crystalline silicon-based film inwhich the percentage of diffraction strength on (220) plane is over 23%has an orientation property in the direction of (220) plane. Inparticular, in the structure in which the percentage of diffractionstrength on (220) plane is 30% or more, the effect of improving themobility of a carrier is considered to become greater.

[0029] Moreover, because the sensitivity especially in the longerwavelength side is increased owing to the optical confinement effect byforming the above described silicon-based semiconductor film on anuneven shape, when an i-type semiconductor layer that practicallyfunctions as a light absorbing layer in a photovoltaic element is formedon the above described uneven shape, there is such a merit that the thinfilm formation of an i-type semiconductor layer is possible. Inparticular, in order to estimate the optical confinement effect to lightin the visible light region, it has been found that the opticalconfinement effect becomes more conspicuous by examining thedistribution of the inclination arctan (df/dx) in the range where thesampling length dx of the cross-sectional shape f of the surface is from20 nm to 100 nm and making the shape with the standard deviation of 15°to 55°.

[0030] On the other hand, when a silicon-based film showing anorientation property and comprising a columnar structure in thethickness direction is formed on the above described uneven shape,because the columnar structure grows in the direction normal to theunevenness of the substrate, the collision of crystal grains and thelike are occurred in the growth process and structural unmatching(inconsistency) is easily caused. In case of a silicon-based film inwhich a Raman scattering strength resulting from an amorphous componentis not exceeding a Raman scattering strength resulting from acrystalline component, it is more difficult to absorb the structuralunmatching in the film forming process as compared to the case of asilicon-based film comprising an amorphous component more abundantly,which component is possible to make the structure more flexible.

[0031] Furthermore, the degree of relaxing the structural unmatching bythe volume diffusion and the surface diffusion effected using thesurface chemical potential induced by recesses and protrusions as adriving force is also low in the tetra-coordination structure like adiamond structure represented by a silicon-based film as compared tothose in single cubic lattice of hexa-coordination, body-centered cubiclattice of octa-coordination, face-centered cubic lattice ofdodeca-coordination and others. For that purpose, in case of asilicon-based film in which a Raman scattering strength resulting froman amorphous component is not exceeding a Raman scattering strengthresulting from a crystalline component, it becomes effective to relaxthe structural unmatching by changing the ratio of lattice constants inthe directions parallel to and perpendicular to the growing surface andby changing the crystal structure to a pseudo-tetragonal crystalstructure.

[0032] Hereby, it is possible to retard the generation of irregulargrain boundaries and dislocations among crystal grains. Throughretarding the generation of these which are regions with nocrystallographical regularity, the lowering of electric activity ingrain boundaries and the retarding of the generation of dangling bondswithin the bulk are realized, as a result, it becomes possible toimprove the mobility of carriers as a silicon-based film.

[0033] However, when the lattice constants are changed, if the degree ofthe change is too large, it will become a factor of lowering themobility of carriers because of inducing point defects within the bulk,there is a limit in the amount that can be changed. Furthermore, whenthe above described standard deviation is smaller than 15°, it is neededto make the i-type semiconductor layer relatively thick because theoptical confinement effect is weak, and when the above describedstandard deviation is over 55°, a steep peak appears, which causes sucha problem that the peak becomes a factor to generate local stress withinthe silicon-based film. Moreover, within the standard deviation of 15°to 55°, it is more preferable to be 20° to 50°, and further morepreferable to be 25° to 40°.

[0034] The present inventor has eagerly conducted studies repeatedly andhas resulted in finding that the area, in which the optical confinementeffect acts effectively, the mobility of carriers within the bulk isfavorably kept and no local stress will be generated within asilicon-based film, is formed on the surface of a substrate where theabove described standard deviation is 15° to 55°, and is such a areathat the difference between the spacing in the direction parallel to theprincipal surface of the above described substrate in the abovedescribed silicon-based film and the spacing of single crystal siliconis within the range of 0.2% to 1.0% on the basis of the spacing of thesingle crystal silicon.

[0035] A method of preparing a substrate that has the surface shape inwhich the standard deviation of the inclination arctan (df/dx) is 15° to55° in the range where the sampling length dx of the cross-sectionalshape f of the surface is from 20 nm to 100 nm will be explained in thefollowing using a means of preparing the above described shape on asubstrate, which is comprised of a SUS substrate, a metal layer and thefirst transparent conductive layer, as an example. About an unevenshape, it may be devised to make uneven shapes in all layers of the SUSsubstrate, the metal layer and the first transparent conductive layer,and also an uneven shape may be formed on only part of them. In otherwords, there is no problem as long as the final surface shape meets theabove described conditions.

[0036] As a method of making an uneven shape on the surface of a SUSsubstrate, the following methods can be included; a method in which heattreatment, acid cleaning and the like are conducted after cold rolling,a rolling method using a roll with a mechanically roughened surface, agrinding method using a belt on which abrasive is applied, methods inwhich the above methods are combined, and others. As a method of makingunevenness on the surface of a metal layer, the following methods can beincluded; a vapor deposition method of a metal layer on a substrateheated to high temperature, a forming method with the use of asputtering method, an electrodeposition method, a printing method andothers. As a method of making unevenness on the surface of the firsttransparent conductive layer, the following methods are included; avapor deposition method of the first transparent conductive layer on asubstrate heated to high temperature, a forming method with the use of asputtering method, an electrodeposition method with the use of asolution containing nitric ions and zinc ions (the concentration is0.001 to 1.0 mol/L, and the liquid temperature is 5° C. or more) and thelike, a printing method and others. When unevenness is made on thesurface of the first transparent conductive layer with a sputteringmethod, it is also effective to introduce oxygen into the feed gas inthe early stage of the forming. Further, in each process using thesemethods, grinding by dry etching, wet etching, sandblasting and thelike, heat treatment and others may be added. In case of using wetetching, the standard deviation can be controlled by controlling wettime. The value of the standard deviation will be increased as thepassage of wet time.

[0037]FIG. 6 is a schematic diagram showing the surface of the abovedescribed shape that was observed with a probe microscope, using whichobserved data, the inclination arctan (df/dx) was obtained from theslope df/dx of the cross-sectional shape f in an optional samplinglength and the distribution of the inclinations was obtained. In therange of shorter sampling lengths, slopes of unevenness not contributingto the optional confinement effect may be measured. Conversely in therange of longer sampling lengths, unevenness corresponding towavelengths contributing to the optional confinement effect cannot becorrectly evaluated because the sampling length and the pitch of theunevenness are close to each other. Consequently, the sampling length ispreferable to be about ⅓ to {fraction (1/10)} of the wavelength of thelight intended to absorb. Generally, when the range of ultravioletlight, visible light and near-infrared light is aimed at, the samplinglength is preferable to be 20 nm to 100 nm. In the present invention,the difference between the spacing in the direction parallel to theprincipal surface of the substrate and the spacing of single crystalsilicon is within the range of 0.2% to 1.0% on the basis of the spacingof the single crystal silicon. If the value is less than 0.2%, it isinsufficient to relax the structural unmathcin, and if the value is morethan 1.0%, it will become a factor of lowering the mobility of carriersbecause of inducing point defects within the bulk and others. This valueis more preferable to be 0.3% to 0.7%. Still more, the term “spacing ofsingle crystal silicon” used herein shall mean a general spacing ofsingle crystal silicon, and shall not mean that the film of the presentinvention comprises single crystal silicon.

[0038] As a means of forming a silicon-based semiconductor film so thatthe difference between the spacing in the direction parallel to theprincipal surface of the above described substrate of a silicon-basedfilm and the spacing of single crystal silicon is within the range of0.2% to 1.0% relative to the spacing of the single crystal silicon witha plasma CVD method using a high frequency, the following means can beincluded. That is, a means in which it becomes possible to more activateion bombardment to allow adhering silicon atoms to act as a part of thesource of a driving force that promotes the displacement of the siliconatoms to the atomic positions in the early stage of the film formationand possible to form a silicon-based film having a crystal structurecorresponding to the surface shape, and others. The more active the ionbombardment is, the higher the above described value becomes.

[0039] Moreover, there is such merits that etching effect acts on thesurface layer to clean the surface by making the ion bombardment moreactive in the early stage of the film formation and as a result, theadhesion between the underlying layer (the layer on which asilicon-based film of the present invention is formed) and thesilicon-based film is increased. In addition, in the early stage of thefilm formation on the surface layer (the underlying layer) having theabove described cross-sectional shape f of the surface, it is fearedthat an initial film of low quality that adversely affects especiallythe mobility of a carrier may be formed because some local areas wheretemperatures are not sufficient are produced, the amorphization of thefilm is induced by the extreme lowering of surface diffusion, andmoreover the optimization of H amount and the relaxation of structureare insufficient, but it is possible to retard the formation of such aninitial film of low quality because heating effect based on the kineticenergy of ions is activated by making the ion bombardment more active.

[0040] Here, about the above described surface layer, in cases where ani-type semiconductor layer in a photovoltaic element comprises the abovedescribed silicon-based film, when an nip constitution is taken from thesubstrate side, an n-type semiconductor layer or another form of ani-type semiconductor layer is suited, and when a pin constitution istaken from the substrate side, a p-type semiconductor layer or anotherform of an i-type semiconductor layer is suited, but the shape of theabove described surface layer is preferable to be formed according tothe shape of the substrate surface.

[0041] As a method of forming a silicon-based film, which method makesthe ion bombardment more active with the use of the plasma CVD methodusing a high frequency, there can be mentioned various methods,including a method in which a high frequency power to be charged isincreased, a method in which a high-frequency power supply for frequencyin which active species in plasma can follow is used, a method in whichinert gases like He, Ar, Ne and others, which are easily converted intoa plasma, are introduced. The use of these prescriptions in the earlystage of forming the above described silicon-based film makes itpossible to form the film so that the difference between the spacing inthe direction parallel to the principal surface of the substrate for thesilicon-based film and the spacing of single crystal silicon is withinthe range of 0.2% to 1.0% on the basis of the spacing of the singlecrystal silicon.

[0042] In the next place, the components of a photovoltaic element ofthe present invention will be described.

[0043]FIG. 1 is a schematic sectional view showing one example of aphotovoltaic element of the present invention. In the figure, 101 is asubstrate, 102 is a semiconductor layer, 103 is a second transparentconductive layer, and 104 is a collecting electrode. Further, 101-1 is asupport, 101-2 is a metal layer, 101-3 is a first transparent conductivelayer, and these are constituent members of the substrate 101.

[0044] (Support)

[0045] As the support 101-1, a plate member or a sheet member that iscomprised of metal, resin, glass, ceramics, semiconductor bulk or thelike is suitably used. The support may have minute unevenness on itssurface. Such a constitution may be adopted in which a transparentsupport is used and a light is incident from the support side. In such acase, light transmittability may be provided by removing the metal layer101-2 or by forming the metal layer in a very small thickness. Further,when the support is made in a long size, continuous film formation isalso made possible using the roll-to-roll method. In particular,materials having flexibility such as stainless steel, polyimide andothers are suitable as the material of the support 101-1.

[0046] (Metal Layer)

[0047] The metal layer 101-2 has a role as an electrode and a role as areflection layer by which a light reaching the support 101-1 isreflected and reused in the semiconductor layer 102. As the material,Al, Cu, Ag, Au, CuMg, AlSi and the like can be suitably used. As theforming method, a vapor deposition method, a sputtering method, anelectrodeposition method, a printing method and others are suitable. Themetal layer 101-2 is preferable to have an unevenness on its surface, bywhich the optical path length of the reflected light within thesemiconductor layer 102 can be extended and the short circuit currentcan be increased. When the support 101-1 has electric conductivity, themetal layer 101-2 is not needed to be formed.

[0048] (First Transparent Conductive Layer)

[0049] The first transparent conductive layer 101-3 has a role ofincreasing the diffused reflection of an incident light and a reflectedlight to extend the optical path length within the semiconductor layer102. Further, an element in the metal layer 101-2 has a role ofdiffusing or migrating into semiconductor layer 102 to prevent aphotovoltaic element from shunting and further has a role of preventingthe short circuit due to defects of pinholes in the semiconductor layerand others by providing a moderate resistance. Moreover, the firsttransparent conductive layer 101-3 is desirable to have an unevenness onthe surface similarly to the metal layer 101-2. The first transparentconductive layer 101-3 is preferable to be comprised of a conductiveoxide such as ZnO or ITO, and is preferable to be formed using a vapordeposition method, a sputtering method, a CVD method, anelectrodeposition method, or the like. A substance that will change theconductivity may be added in the conductive oxide. When the metal layer101-2 is not prepared, the first transparent conductive layer 101-3 willalso serve as an electrode.

[0050] (Substrate)

[0051] According to the above described method, the metal layer 101-2and the first transparent conductive layer 101-3 are stacked on thesupport 101-1 optionally to form the substrate 101. An insulating layermay be prepared as an intermediate layer within the substrate 101 tomake the accumulation of the elements easy. Now, concerning a substratein the present invention, the metal layer 101-2 and the transparentconductive layer 101-3 are not indispensable, and the support 101-1itself may form the substrate 101. Besides, the term “substrate” isconveniently used herein, and the substrate is not needed to beplate-shaped so long as it has a prescribed surface shape. Moreover, amember having a semiconductor layer formed on a substrate may also bereferred to as a “substrate”.

[0052] (Semiconductor Layer)

[0053] As a major material for the silicon-based film and thesemiconductor layer 102 of the present invention, Si in an amorphousphase, a crystal phase, or further a mixed phase of these is suitablyused. Instead of Si, an alloy of Si and C, Ge or the like may be used.It is preferable for the semiconductor layer 102 to additionally containhydrogen and/or halogen atoms. The preferred content is 0.1 to 40 atomic%. Furthermore, the semiconductor layer 102 may contain oxygen, nitrogenand the like. In order to make a semiconductor layer to be a p-typesemiconductor layer, an element of Group III of the periodic table ispreferable to be contained, and to be an n-type semiconductor layer, anelement of Group V is preferable to be contained.

[0054] As the electrical characteristics of the p-type layer and n-typelayer, the activation energy is preferable to be 0.2 eV or less, andoptimum to be 0.1 eV or less. Further, the resistivity is preferable tobe 100 Ωcm or less, and optimum to be 1 Ωcm or less. In case of a stackcell (a photovoltaic element having a plurality of pin junctions), it ispreferable that an i-type semiconductor layer of a pin junction near thelight incidence side has a wide bandgap and the bandgap becomes narrowerwith increase of the distance of a pin junction from the light incidenceside.

[0055] Further, the minimum value of the bandgap of an i-type layer ispreferable to be near a p-layer with regard to a center in the filmthickness direction within the i layer. The doping layer (a p-type layeror an n-type layer) on the light incidence side is suitable to be acrystalline semiconductor with a low light absorption or a semiconductorhaving a wide bandgap. As examples of a stack cell in which 2 pinjunctions are stacked, a combination of an amorphous semiconductor layerand a semiconductor layer comprising a crystal phase in the order fromthe light incidence side and a combination of a semiconductor layercomprising a crystal phase and a semiconductor layer comprising acrystal phase in the order from the light incidence side can be includedas combinations having an i-type silicon-based semiconductor layer.

[0056] Moreover, as examples of photovoltaic elements in which 3 pinjunctions are stacked, combinations of (an amorphous semiconductorlayer, an amorphous semiconductor layer and a semiconductor layercomprising a crystal phase), (an amorphous semiconductor layer, asemiconductor layer comprising a crystal phase and a semiconductor layercomprising a crystal phase) and (a semiconductor layer comprising acrystal phase, a semiconductor layer comprising a crystal phase and asemiconductor layer comprising a crystal phase) each in the order fromthe light incidence side can be included as combinations having ani-type silicon-based semiconductor layer.

[0057] As an i-type semiconductor layer, it is preferable that theabsorption coefficient (α) of light (630 nm) is 500 cm⁻¹ or more, thephotoconductivity (σp) under irradiation with artificial sunlight by asolar simulator (AM 1.5; 100 mW/cm^(2) is) 10×10⁻⁵ S/cm or more, thedark conductivity (σd) is 10×10⁻⁶ S/cm or less, and the Urbach energymeasured by a constant photocurrent method (CPM) is 55 meV or less. Asan i-type semiconductor layer, a slightly p-type one and a slightlyn-type one can also be used. Further, the pin junction may be aconstitution in the order of a p-layer, an i-layer and an n-layer fromthe substrate side, or that in the reverse order.

[0058] (Method of Forming Semiconductor Layer)

[0059] In order to form a silicon-based film and the describedsemiconductor layer 102 of the present invention, a high-frequencyplasma CVD method is suitable. In the following, a suitable procedurefor forming semiconductor layer 102 according to a high-frequency plasmaCVD method will be described.

[0060] (1) The pressure inside a pressure-reducible deposition chamber(a vacuum chamber) is reduced to a prescribed deposition pressure.

[0061] (2) Material gases, including a source gas and a diluting gas,are introduced into the deposition chamber, and the pressure inside thedeposition chamber is set to be a prescribed pressure while continuingthe exhaust from the deposition chamber with a vacuum pump.

[0062] (3) The substrate 101 is set to be a prescribed temperature witha heater.

[0063] (4) A high frequency oscillated by a high frequency power supplyis introduced into the above described deposition chamber. Theintroduction methods into the above described deposition chamber includea method in which a high frequency is conducted by a waveguide andintroduced into the deposition chamber through a dielectric window ofalumina ceramics and the like, and a method in which a high frequency isconducted by a coaxial cable and introduced into the deposition chamberthrough a metal electrode.

[0064] (5) A plasma is generated in the deposition chamber to decomposethe source gas and a deposition film is formed on the substrate 101arranged within the deposition chamber. The semiconductor layer 102 isformed by repeating this procedure plurality of times if necessary.

[0065] As the conditions of forming the silicon-based film and the abovedescribed semiconductor layer 102 of the present invention, thesubstrate temperature of 100 to 450° C., the pressure of 0.5 mTorr to 10Torr, the high frequency power of 0.001 to 1 W/cm³ within the depositionchamber are mentioned as suitable conditions.

[0066] As the source gases that are suitable for forming thesilicon-based film and the above described semiconductor layer 102 ofthe present invention, gasifiable compounds containing silicon atom,including SiH₄, Si₂H₆ and SiF₄, can be included. When an alloy-basedfilm and/or an alloy-based semiconductor layer is formed, further agasifiable compound containing Ge or C, including GeH₄ and CH₄, isdesirable to be added into a feed gas. A source gas is desirable to bediluted with a diluting gas and introduced into the deposition chamber.As the diluting gas, H₂, He, Ar, Ne and the like can be listed. Further,a gasifiable compound containing nitrogen, oxygen and the like may beadded as a source gas or a diluting gas. In order to attain that a Ramanscattering strength resulting from an amorphous component be notexceeding a Raman scattering strength resulting from a crystallinecomponent, there can be included some methods, including a method ofraising the flow rate ratio of H₂ gas to SiH₄ gas, a method of raisingtemperature for film formation, and a method of using a gas containingan element of halogens like SiF₄ and others as a source gas.

[0067] As the dopant gas to make the semiconductor layer be a p-typelayer, B₂H₆, BF₃ and the like are used. Further, as the dopant gas tomake the semiconductor layer be an n-type layer, PH₃, PF₃ and the likeare used.

[0068] When a film of a crystal phase, and a layer of SiC and the likewith low light absorption or having a wide bandgap are deposited, it ispreferable to increase the ratio of a diluting gas to a source gas andto introduce a high frequency with a relatively high power. Further, inorder to form a silicon-based film of the present invention so that thedifference between the spacing in the direction parallel to the abovedescribed substrate and the spacing of single crystal silicon is withinthe range of 0.2% to 1.0% on the basis of the spacing of single crystalsilicon, it is considered that as described above, it becomes possibleto more activate ion bombardment to allow adhering silicon atom to actas a part of the source of a driving force that promotes thedisplacement of the silicon atoms to the atomic positions in the earlystage of the film formation and possible to form a silicon-based filmhaving a crystal structure corresponding to the surface shape. As amethod of forming a silicon-based film, which method makes ionbombardments more active with the use of the plasma CVD method using ahigh frequency, there can be included various methods, including amethod in which a high frequency power to be charged is increased, amethod in which a high-frequency power supply for frequency in whichactive species in a plasma can follow is used, a method in which aninert gas like He, Ar, Ne and others, which is easily converted to aplasma, is introduced. The high frequency in the plasma CVD method ispreferable to be from 10 MHz or more to 10 GHz or less. Further, in theabove described range and in the initial area of film forming, it ispreferable to form a film using a relatively low frequency so thatactive species in plasma can easily follow.

[0069] (Second Transparent Conductive Layer)

[0070] In an example shown in FIG. 1, the second transparent conductivelayer 103 can serve for the role of an antireflection film by properlysetting the film thickness, as well as being an electrode in the lightincidence side. The second transparent conductive layer 103 is needed tohave a high transmittance in a wavelength area that semiconductor layer102 can absorb and to be low in resistivity. It is desirable that thetransmittance at 550 nm is preferable to be 80% or more, and morepreferably 85% or more. It is preferable that the resistivity is 5×10⁻³Ωcm or less, and more preferably 1×10⁻³ Ωcm or less. As the material forthe second transparent conductive layer 103, ITO, ZnO, In₂O₃ and otherscan be suitably used. As the methods of forming the layer, methods ofvapor deposition, CVD, spraying, spin-on, dipping and others aresuitable. A substance for changing conductivity may be added in thesematerials.

[0071] (Collecting electrode)

[0072] The collecting electrode 104 is provided on the transparentelectrode 103 to improve the current collecting efficiency. As theforming methods, a method of forming a metal of an electrode pattern bya sputtering with a mask, a method of printing a conductive paste orsoldering paste, a method of firmly fixing a metal wire using aconductive paste, and others are suitable.

[0073] Moreover, a protective layer may be formed on both surface of aphotovoltaic element if necessary. At the same time, a reinforcingmaterial, including a steel plate, may be used together on the back ofthe photovoltaic element (the light incidence side and the reflectionside) and the like.

EXAMPLES

[0074] In the following examples, the present invention will beconcretely described with reference to a solar cell as a photovoltaicelement, but these examples are not intended to limit the contents ofthe present invention.

Example 1

[0075] A silicon-based film was formed according to the followingprocedure using a deposited film forming apparatus 201 shown in FIG. 2.

[0076]FIG. 2 is a schematic sectional view showing one example of adeposited film forming apparatus to produce a silicon-based film and aphotovoltaic element of the present invention. The deposited filmforming apparatus 201 shown in FIG. 2 is constituted by combiningsubstrate a delivery container 202, vacuum containers 211 to 218 forforming a semiconductor and a substrate winding container 203 by meansof gas gates 221 to 229. In this deposited film forming apparatus 201, abelt-like conductive substrate 204 is set through each container andeach gas gate 221 to 229. The belt-like conductive substrate 204 iswound off from a bobbin installed in the substrate delivery container202 and is wound up by another bobbin in the substrate winding container203.

[0077] Vacuum containers 211 to 218 for forming a semiconductor have adeposition chamber each, and a glow discharge was occurred by applying ahigh frequency electric power from high frequency power supplies 251 to258 to the discharge electrodes 241 to 248 in the discharge chamber, bywhich the source gas was decomposed and a semiconductor layer wasdeposited on conductive substrate 204. Further, gas introduction pipes231 to 238 for introducing the source gas and a diluting gas areconnected to vacuum containers 211 to 218 for forming a semiconductor,respectively.

[0078] The deposited film forming apparatus 201 shown in FIG. 2 isprovided with 8 vacuum containers for forming a semiconductor. However,in the following examples, a glow discharge is not needed to occur inall of the vacuum containers for forming a semiconductor, and it ispossible to select the presence or absence of a glow discharge in eachcontainer according to the layer composition of a photovoltaic elementto be produced. Further, a film forming region adjusting plate, which isnot shown in the figure, is provided in each semiconductor formingdevice to adjust the contact area between the conductive substrate 204and the discharge space in each deposition chamber, and the filmthickness of each semiconductor film formed in each container can beadjusted by adjusting the plate.

[0079] First, a belt-like substrate (40 cm in width, 200 m in length,and 0.125 mm in thickness) made of stainless steel (SUS430BA) wassufficiently degreased, washed, and installed in a continuous sputteringdevice, which is not shown in the figure, and then an Ag thin film of100 nm in thickness was deposited by sputtering at room temperature,using an Ag electrode as a target.

[0080] In addition, using a ZnO target, a ZnO thin film of 1.2 μm inthickness was deposited on the Ag thin film by sputtering to form abelt-like conductive substrate 204. Next, the substrate 204 wasinstalled in a wet etcher, which is not shown in the figure, and dippedin a 5% acetic acid solution for 30 seconds, and then the substrate 204was sufficiently washed and dried. A part of the prepared conductivesubstrate 204 was cut off and the cross-sectional shape of the surfacewas observed with a probe microscope, and when the distribution of theinclinations in the cross section was found, the standard deviation was20°.

[0081] In the next place, a bobbin on which the conductive substrate 204had been wound was installed in the substrate delivery container 202,and the conductive substrate 204 was passed to the substrate windingcontainer 203 through a gas gate in the carrying-in side, the vacuumcontainers 211, 212, 213, 214, 215, 216, 217, and 218 for forming asemiconductor, and a gas gate in the carrying-out side. Further, thetension was adjusted so that the belt-like conductive substrate 204would not be loosened. After that, the substrate delivery container 202,the vacuum containers 211, 212, 213, 214, 215, 216, 217, and 218 forforming a semiconductor, and the substrate winding container 203 weresufficiently evacuated to 5×10⁻⁶ Torr with a vacuum pumping systemcomprising a vacuum pump.

[0082] Next, while the vacuum pumping system was operated, a source gasand a diluting gas were provided from gas the introduction pipes 232,233, and 234 to the vacuum containers 212, 213, and 214 for forming asemiconductor.

[0083] Furthermore, H₂ gas of 200 sccm was supplied to the vacuumcontainers for forming a semiconductor except the vacuum containers 212,213, and 214 for forming a semiconductor through the gas introductionpipes. At the same time, H₂ gas of 500 sccm was provided to each gasgate as a gate gas through each gate gas feed pipe, which is not shownin the figure. In this state, the pressure inside the vacuum containers212, 213, and 214 for forming a semiconductor was adjusted to thedesired pressure by adjusting the pumping performance of the vacuumpumping system. The forming conditions are as shown in Table 1.

[0084] After the pressures inside the vacuum containers 212, 213, and214 for forming a semiconductor were stabilized, the conductivesubstrate 204 was started to move in the direction from the substratedelivery container 202 to the substrate winding container 203. While theconductive substrate 204 was moved, a high frequency was introduced tothe discharge electrodes 242, 243, and 244 in the vacuum containers 212,213, and 214 for forming a semiconductor from the high frequency powersupplies 252, 253, and 254, and glow discharges were generated withinthe deposition chambers in the vacuum containers 212, 213, and 214 forforming a semiconductor to form an i-type semiconductor layer comprisinga crystal phase (1.5 μm in thickness: a silicon-based film) on theconductive substrate 204 (Example 1). Here, the high-frequency electricpower of 100 MHz in frequency and 20 mW/cm³ in power was introduced inthe vacuum containers 212, 213, and 214 for forming a semiconductor.

[0085] Next, a silicon-based film was formed by the same method asExample 1, except for Ar was not introduced in the vacuum container 212for forming a semiconductor in Table 1 (Comparative example 1).

[0086] In the next place, when diffraction peaks were measured insilicon-based films prepared in Example 1 and Comparative example 1 bythe θ-2θ method with an X-ray diffraction system and the spacing of the(220) plane was found from 2θ position in the diffraction peak of 220reflection in each film, as compared to the spacing of the (220) planein single crystal silicon of 1.9201 Å that was found from the X-raydiffractometry, the spacing in the silicon-based film of Example 1 waswider by 0.4%, and the spacing in the silicon-based film of Comparativeexample 1 was about the same value as single crystal silicon.

[0087] Moreover, the density of dangling bonds in the silicon-basedfilms was evaluated by the electron spin resonance (ESR) method,resulting in that the density of dangling bonds in the silicon-basedfilm prepared in Example 1 was two-thirds of the density of danglingbonds in the silicon-based film prepared in Comparative example 1. Fromthe above results, it is seen that the silicon-based film of the presentinvention is characterized by a small density of dangling bonds and anexcellent mobility of carriers.

Example 2

[0088] A silicon-based film was formed on a conductive substrate 204similarly to Example 1 using the deposited film forming apparatus 201shown in FIG. 3. The forming conditions are as shown in Table 2.

[0089] After the pressures inside the vacuum containers 212, 213, and214 for forming a semiconductor were stabilized, the conductivesubstrate 204 was started to move, in the direction from the substratedelivery container 202 to the substrate winding container 203. While theconductive substrate 204 was moved, a high frequency was introduced todischarge electrodes 242, 243, and 244 in the vacuum containers 212,213, and 214 for forming a semiconductor from the high frequency powersupplies 252, 253, and 254, and glow discharges were generated withinthe deposition chambers in the vacuum containers 212, 213, and 214 forforming a semiconductor to form an i-type semiconductor layer comprisinga crystal phase (1.5 μm in thickness: a silicon-based film) on theconductive substrate 204 (Example 2).

[0090] Here, the high-frequency electric power of 13.56 MHz in frequencyand 30 mW/cm³ in power was introduced in the vacuum container 212 forforming a semiconductor, and the high-frequency electric power of 2.45GHz in frequency and 50 mW/cm³ in power was introduced in the vacuumcontainers 213 and 214 for forming a semiconductor through microwaveapplicators 261 and 262.

[0091] In the next place, when a diffraction peak was measured in thesilicon-based film prepared in Example 2 by the θ-2θ method with anX-ray diffraction system and the spacing of the (220) plane was foundfrom 2θ position in the diffraction peak of 220 reflection, as comparedto the spacing of the (220) plane in single crystal silicon of 1.9201 Åthat was found from the X-ray diffractometry, the spacing in thesilicon-based film of Example 2 was 0.78% wider.

[0092] Moreover, the density of dangling bonds in the silicon-based filmwas evaluated by the electron spin resonance (ESR) method, resulting inthat the density of dangling bonds in the silicon-based film prepared inExample 2 was three-fifths of the density of dangling bonds in thesilicon-based film prepared in Comparative example 1. From the aboveresults, it is known that a silicon-based film of the present inventionis low in density of dangling bonds and has an excellent property in themobility of a carrier.

Example 3

[0093] A pin-type photovoltaic element shown in FIG. 4 was formedaccording to the following procedure using the deposited film formingapparatus 201 shown in FIG. 2. FIG. 4 is a schematic sectional viewshowing one example of a photovoltaic element comprising a silicon-basedfilm of the present invention. In the figure, the same members as thosein FIG. 1 will be marked with the same symbols and their descriptionwill be omitted. The semiconductor layer of this photovoltaic element iscomprised of an amorphous n-type semiconductor layer 102-1, an i-typesemiconductor layer 102-2 comprising microcrystals, and amicrocrystalline p-type semiconductor layer 102-3. That is, thisphotovoltaic element is a so-called pin-type single cell photovoltaicelement.

[0094] Similarly to Example 1, a belt-like conductive substrate 204 wasprepared and installed in the deposited film forming apparatus 201, andthe substrate delivery container 202, the vacuum containers 211, 212,213, 214, 215, 216, 217, and 218 for forming a semiconductor, and thesubstrate winding container 203 were sufficiently evacuated to 5×10⁻⁶Torr or less with a vacuum pumping system comprising a vacuum pump notshown in the figure.

[0095] Next, while the vacuum pumping system was operated, a source gasand a diluting gas were provided from the gas introduction pipes 231 to235 to the vacuum containers 211 to 215 for forming a semiconductor.

[0096] Furthermore, H₂ gas of 200 sccm was supplied to the vacuumcontainers for forming a semiconductor except the vacuum containers 211to 215 for forming a semiconductor through the gas introduction pipes.At the same time, H₂ gas of 500 sccm was provided to each gas gate as agate gas through each gate gas feed pipe, which is not shown in thefigure. At this condition, the pressures inside the vacuum containers211 to 215 for forming a semiconductor were adjusted to the desiredpressures by adjusting the pumping performance of the vacuum pumpingsystem. The forming conditions are as shown in Table 3.

[0097] Next, through the introduction of a high frequency into thedischarge electrodes 241 to 245 within the vacuum containers 211 to 215for forming a semiconductor from high frequency power supplies 251 to255, glow discharges were generated within deposition chambers in thevacuum containers 211 to 215 for forming a semiconductor and anamorphous n-type semiconductor layer (30 nm in film thickness), ani-type semiconductor layer comprising a crystal phase (1.5 μm in filmthickness) and a microcrystalline p-type semiconductor layer (10 nm infilm thickness) were formed on the conductive substrate 204, resultingin the formation of a photovoltaic element.

[0098] Here, the high frequency electric power of 13.56 MHz in frequencyand 50 mW/cm³ in power was introduced in the vacuum container 211 forforming a semiconductor, the electric power of 100 MHz in frequency and20 mW/cm³ in power was in the vacuum containers 212, 213 and 214 forforming a semiconductor, and the electric power of 13.56 MHz infrequency and 30 mW/cm³ in power was in the container 215 for forming asemiconductor. Next, using a continuous modularizing apparatus not shownin the figure, the formed belt-like photovoltaic element was processedto be a solar cell module of 36 cm×22 cm in size (Example 3).

[0099] Next, a solar cell module was formed by the same method asExample 3, except for Ar was not introduced in the vacuum container 212for forming a semiconductor

(Comparative example 3).

[0100] The photoelectric conversion efficiencies of the solar cellmodules prepared in Example 3 and Comparative example 3 were measuredusing a solar simulator (AM 1.5, 100 mW/cm²). When the photoelectricconversion efficiency of the solar cell module formed in Example 3 wasstandardized (normalized) to be 1, the value of the photoelectricconversion efficiency of the solar cell module formed in Comparativeexample 3 was 0.90.

[0101] Further, the adhesion between the conductive substrate and thesemiconductor layer was examined with the use of the cross cut tape testmethod (the gap width of cut is 1 mm, the number of squares is 100).Further, a solar cell module of which the initial photoelectricconversion efficiency had been measured in advance was put in a darkplace, where the temperature was 85° C. and the humidity was 85%, andkept for 30 minutes, then the temperature was lowered to −20° C. in 70minutes and the module was kept at the temperature for 30 minutes, andthen the temperature was again returned to 85° C. and humidity to 85% in70 minutes. After this cycle was repeated 100 times, the photoelectricconversion efficiency was measured again and the variation of thephotoelectric conversion efficiency as a result of the temperature andhumidity test was examined.

[0102] Furthermore, after a solar cell module of which the initialphotoelectric conversion efficiency had been measured in advance waskept at 50° C. and irradiated with an artificial sunlight (AM 1.5, 100mW/cm²) for 500 hours, the photoelectric conversion efficiency wasmeasured again and the variation of the photoelectric conversionefficiency as a result of the photodegradation test was examined. Theseresults are shown in Table 4.

[0103] As shown in Table 4, the solar cell module of Example 3, whichcomprises a photovoltaic element of the present invention, is excellentin the initial conversion efficiency, the adhesion, and the durabilityin the temperature and humidity test and the photodegradation test, whencompared to the solar cell module of Comparative example 3. From theabove results, it is seen that a solar cell module comprising aphotovoltaic element of the present invention has excellent properties.

Example 4

[0104] First, similarly to Example 1, a belt-like substrate (40 cm inwidth, 200 m in length, and 0.125 mm in thickness) made of stainlesssteel (SUS430BA) was sufficiently degreased, washed, and installed in acontinuous sputtering apparatus, which is not shown in the figure, andthen an Ag thin film of 100 nm in thickness was deposited by sputteringat room temperature, using Ag electrode as a target. In addition, usinga ZnO target, a ZnO thin film of 1.2 μm in thickness was deposited onthe Ag thin film by sputtering to form belt-like conductive substrate204. Next, the conductive substrate 204 was installed in a wet etcher,which is not shown in the figure, and wet etched in 5% acetic acidsolution so that the standard deviation of inclinations in the crosssection became to be 15°, 20°, 25°, 40°, 50°, and 55° while changingtime. Then, the wet etched substrate 204 was sufficiently washed anddried. After that, a pin-type photovoltaic element was formed similarlyto Example 3 using deposited film forming apparatus 201 shown in FIG. 2(Example 4-1 to 4-6).

[0105] After wet etching was carried out in the same way so that thestandard deviation of inclinations in the cross section became to be 5°and 60° while changing time, the substrate was sufficiently washed anddried. After that, a pin-type photovoltaic element was made similarly toExample 3 using the deposited film forming apparatus 201 shown in FIG. 2(Comparative example 4-1 and 4-2).

[0106] A hundred pieces of transparent conductive layers (ITO) 103 intotal were prepared in the circular shape having 1 cm² area on asemiconductor layer by masking as shown in FIG. 7 and served assubcells, and a collecting electrode was prepared on each subcell. Thesolar cell characteristics of these subcells were measured with a solarsimulator (AM 1.5; 100 mW/cm²; 25° C. in surface temperature), and theshunt resistances of 100 pieces of subcells of each solar cell wasmeasured. A subcell having a practically needed shunt resistance wasjudged to be a surviving subcell, the yield was evaluated based on thenumber of surviving subcells, and the yield of each photovoltaic elementwas compared. When the number of surviving subcells in Example 4-1 wasstandardized to be 1, the number of surviving cells in each photovoltaicelement is shown in Table 5.

[0107] Further, the average value of the photoelectric conversionefficiency values of the surviving subcells in each photovoltaic elementwas calculated. When the photoelectric conversion efficiency of thesolar cell module in Example 4-1 was standardized to be 1, thephotoelectric conversion efficiency of each photovoltaic element isshown in Table 5.

[0108] As shown in Table 5, the average value of the photoelectricconversion efficiency was low in Comparative example 4-1. Because theshort circuit current in Comparative example 4-1 was 0.85 when the shortcircuit current in Example 4-1 was standardized to be 1, the loweredpart of the photoelectric conversion efficiency is considered to becaused by the decrease in the short circuit current due to insufficientoptical confinement effect. Further, the number of surviving subcellswas small in Comparative example 4-2. The reason is considered that asteep peak was generated in the surface of the conductive substrate togenerate local stress within the silicon-based film.

[0109] From the above results, it is seen that a photovoltaic element ofthe present invention has excellent properties.

Example 5

[0110] A photovoltaic element shown in FIG. 5 was formed according tothe following procedure using the deposited film forming apparatus 201shown in FIG. 2. FIG. 5 is a schematic sectional view showing oneexample of a photovoltaic element comprising a silicon-based film of thepresent invention. In the figure, the same members as those in FIG. 1will be marked with the same symbols and their description will beomitted. The semiconductor layer of this photovoltaic element iscomprised of an amorphous n-type semiconductor layer 102-1, an i-typesemiconductor layer 102-2 comprising microcrystals, a microcrystallinep-type semiconductor layer 102-3, an amorphous n-type semiconductorlayer 102-4, an amorphous i-type semiconductor layer 102-5, and amicrocrystalline p-type semiconductor layer 102-6. That is, thisphotovoltaic element is a so-called pinpin-type double cell photovoltaicelement.

[0111] Similarly to Example 3, a belt-like conductive substrate 204 wasprepared and installed in the deposited film forming apparatus 201, andthe substrate delivery container 202, the vacuum containers 211, 212,213, 214, 215, 216, 217, and 218 for forming a semiconductor, and thesubstrate winding container 203 were sufficiently evacuated to 5×10⁻⁶Torr or less with a vacuum pumping system comprising a vacuum pump notshown in the figure.

[0112] Next, while the vacuum pumping system was operated, a source gasand a diluting gas were supplied from the gas introduction pipes 231 to238 to the vacuum containers 211 to 218 for forming a semiconductor.

[0113] Furthermore, H₂ gas of 500 sccm was supplied to each gas gate asa gate gas through each gate gas feed pipe, which is not shown in thefigure. In this state, the pressures inside the vacuum containers 211 to218 for forming a semiconductor were adjusted to the desired pressuresby adjusting the pumping performance of the vacuum pumping system. Theformation of the bottom cell was carried out similarly to Example 3, theformation of the n layer and the p layer in the top cell was carried outsimilarly to Example 3, and the formation of the i-type semiconductorlayer in the top cell was carried out in such conditions that SiH₄ is 50sccm, H₂ is 500 sccm, the substrate temperature is 220° C., and thepressure is 1.2 Torr.

[0114] After the pressures within the vacuum containers 211 to 218 forforming a semiconductor were stabilized, the conductive substrate 204was started to move in the direction from the substrate deliverycontainer 202 to the substrate winding container 203.

[0115] Next, through the introduction of high-frequency in dischargeelectrodes 241 to 248 within the vacuum containers 211 to 218 forforming a semiconductor from high-frequency power supplies 251 to 258,glow discharges were generated within deposition chambers in the vacuumcontainers 211 to 218 for forming a semiconductor and an amorphousn-type semiconductor layer (30 nm in film thickness), an i-typesemiconductor layer comprising a crystal phase (2.0 μm in filmthickness) and a microcrystalline p-type semiconductor layer (10 nm infilm thickness) were formed on the conductive substrate 204, resultingin the preparation of the bottom cell, on which cell further anamorphous n-type semiconductor layer (30 nm in film thickness),amorphous i-type semiconductor layer (0.3 μm in film thickness) and amicrocrystalline p-type semiconductor layer (10 nm in film thickness)were formed, resulting in the preparation of the top cell, and as aresult, a photovoltaic element was formed.

[0116] Here, the high frequency electric power of 13.56 MHz in frequencyand 5 mW/cm³ in power was introduced in the vacuum container 211 forforming a semiconductor, the electric power of 100 MHz in frequency and20 mW/cm³ in power was in the vacuum containers 212, 213 and 214 forforming a semiconductor, the electric power of 13.56 MHz in frequencyand 30 mW/cm³ in power was in the container 215 for forming asemiconductor, the electric power of 13.56 MHz in frequency and 5 mW/cm³in power was in the vacuum containers 216 and 217 for forming asemiconductor, and the high-frequency electric power of 13.56 MHz infrequency and 30 mW/cm³ in power was introduced in the vacuum container218 for forming a semiconductor.

[0117] Next, using a continuous modularizing apparatus not shown in thefigure, the formed belt-like photovoltaic element was processed to be asolar cell module of 36 cm×22 cm in size (Example 5).

[0118] The solar cell module of Example 5 showed 1.2 times higherphotoelectric conversion efficiency when compared to the solar cellmodule of Example 3, and the solar cell module of Example 5 is excellentin adhesion and in durability in the temperature and humidity test andthe photodegradation test. From the above results, it is seen that asolar cell module comprising a photovoltaic element of the presentinvention has excellent properties.

Example 6

[0119] Solar cell modules were formed by the same method as Example 3and Comparative example 3, except for high frequency power to beintroduced in the vacuum container 212 for forming a semiconductor waschanged (Example 6-1 to 6-5, and Comparative example 6-1 to 6-2). Thespacing of the (220) plane in the i-type semiconductor layer of eachsolar cell module was found to be wider in the range of 0.1% to 1.5%, ascompared to the spacing in single crystal silicon that was found fromthe X-ray diffractometry.

[0120] The photoelectric conversion efficiencies of the solar cellmodules prepared in Example 6 and Comparative example 6 were measuredusing a solar simulator (AM 1.5, 100 mW/cm²).

[0121] Further, the adhesion between the conductive substrate and thesemiconductor layer was examined with the use of the cross cut tape testmethod (the gap width of cut is 1 mm, the number of squares is 100).Further, a solar cell module of which the initial photoelectricconversion efficiency had been measured in advance was put in a darkplace, where the temperature was 85° C. and the humidity was 85%, andkept for 30 minutes, then the temperature was lowered to −20° C. in 70minutes and the module was kept at the temperature for 30 minutes, andthen the temperature was again returned to 85° C. and humidity to 85% in70 minutes. After this cycle was repeated 100 times, the photoelectricconversion efficiency was measured again and the variation of thephotoelectric conversion efficiency as a result of the temperature andhumidity test was examined.

[0122] Furthermore, after a solar cell module of which the initialphotoelectric conversion efficiency had been measured in advance waskept at 50° C. and irradiated with an artificial sunlight (AM 1.5, 100mW/cm²) for 500 hours, the photoelectric conversion efficiency wasmeasured again and the variation of the photoelectric conversionefficiency as a result of the photodegradation test was examined. Theseresults are shown in Table 6.

[0123] The numeral values in the column of the spacing of the (220)plane indicate expanded rates as compared to the spacing of the surfacein single crystal silicon that was found from the X-ray diffractometry.

[0124] As shown in Table 6, the solar cell modules in which the spacingof the (220) plane in the i-type semiconductor layer was found to bewider in the range of 0.2% to 1.0% as compared to the spacing in singlecrystal silicon that was found from the X-ray diffractometry areexcellent in the initial conversion efficiency, the adhesion, and thedurability in the temperature and humidity test and the photodegradationtest, when compared to the solar cell modules of Comparative example.From the above results, it is seen that a solar cell module comprising aphotovoltaic element of the present invention has excellent properties.

[0125] As described above, the preferred embodiments of the presentinvention makes it possible to provide a silicon-based film that isexcellent in the mobility of carriers even on the surface, and aphotovoltaic element comprising the silicon-based film improves inadhesion with a substrate and shows good environmental resistancebecause good photoelectric conversion characteristics are obtained,crack generating factors in the film can be suppressed, and the formedsurface is cleaned. TABLE 1 Formation Source gases SiH₄: 30 sccmconditions H₂: 1000 sccm of 212 Ar: 100 sccm Substrate 300° C.temperature Pressure 300 mTorr Formation Source gases SiH₄: 30 sccmconditions H₂: 1000 sccm of 213 and Substrate 300° C. 214 temperaturePressure 300 mTorr

[0126] TABLE 2 Formation Source gases SiH₄: 30 sccm conditions H₂: 1000sccm of 212 Substrate 200° C. temperature Pressure 300 mTorr FormationSource gases SiH₄: 30 sccm conditions H₂: 1000 sccm of 213 and Substrate300° C. 214 temperature Pressure 300 mTorr

[0127] TABLE 3 Formation Source gases SiH₄: 20 sccm conditions H₂: 100sccm of 211 PH₃(diluted with H₂ to 2%): 30 sccm Substrate 300° C.temperature Pressure 1.0 Torr Formation Source gases SiH₄: 30 sccmconditions H₂: 1000 sccm of 212 Ar: 100 sccm Substrate 300° C.temperature Pressure 300 mTorr Formation Source gases SiH₄: 30 sccmconditions H₂: 1000 sccm of 213 and Substrate 300° C. 214 temperaturePressure 300 mTorr Formation Source gases SiH₄: 10 sccm conditions H₂:800 sccm of 215 BF₃(diluted with H₂ to 2%): 100 sccm Substrate 200° C.temperature Pressure 1.2 Torr

[0128] TABLE 4 Comparative Example 3 Example 3 Initial photoelectricconversion efficiency 1 0.90 Number of surviving squares in cross cuttape 1 0.95 test (normalized with the value for Example 3 being 1)Variation of photoelectric conversion efficiency 1.0 0.95 intemperature-humidity test (efficiency after test/initial efficiency)Variation of photoelectric conversion efficiency 1 1.35 inphotodegradation test (normalized with the value for Example 3 being 1)

[0129] TABLE 5 Standard 5° 60° deviation of cross Comp. 15° 20° 25° 40°50° 55° Comp. sectional Ex. Ex. Ex. Ex. Ex. Ex. Ex. Ex. inclination 4-14-1 4-2 4-3 4-4 4-5 4-6 4-2 Number of 1.0 1 1.0 1.0 1.0 1.0 1.0 0.85surviving subcells Photoelectric 0.8 1 1.1 1.2 1.2 1.1 1.0 0.95conversion efficiency

[0130] TABLE 6 Comp. Comp. Ex. Ex. Ex. Ex. Ex. Ex. Ex. 6-1 6-1 6-2 6-36-4 6-5 6-2 High frequency 10 15 18 20 25 30 40 power (mW/cm³) Spacingof (220) 0.1% 0.2% 0.3% 0.4% 0.7% 1.0% 1.5% plane Initial photoelectric0.95 1 1.1 1.2 1.2 1.0 0.85 conversion efficiency (normalized with thevalue for Example 6-1 being 1) Number of 0.90 1 1.1 1.1 1.1 1.0 0.75surviving squares in cross cut tape test (normalized with the value forExample 6-1 being 1) Variation of 0.95 1.0 1.0 1.0 1.0 1.0 0.95photoelectric conversion efficiency in temperature- humidity test(efficiency after test/initial efficiency) Variation of 1.15 1 1.0 1.01.0 1.0 1.10 photoelectric conversion efficiency in photodegradationtest (normalized with the value for Example 6-1 being 1)

What is claimed is:
 1. A silicon-based film comprising a crystal phase formed on a substrate with a surface shape represented by a function f, wherein the silicon-based film is formed on a substrate with a surface shape having a standard deviation of an inclination arctan (df/dx) from 15° to 55° within the range of a sampling length dx from 20 nm to 100 nm, a Raman scattering strength resulting from an amorphous component in the silicon-based film is not more than a Raman scattering strength resulting from a crystalline component, and a difference between a spacing in a direction parallel to a principal surface of the substrate and a spacing of single crystal silicon is within the range of 0.2% to 1.0% with regard to the spacing of the single crystal silicon.
 2. The silicon-based film according to claim 1, comprising a crystal of a columnar structure in a thickness direction.
 3. The silicon-based film according to claim 1, wherein a percentage of a diffraction strength of (220) plane due to X-ray or electron beam diffraction is 30% or more of a total diffraction strength.
 4. The silicon-based film according to claim 1, which is formed by a plasma CVD method using a high frequency.
 5. The silicon-based film according to claim 4, wherein the high frequency is not less than 10 MHz but no more than 10 GHz.
 6. A photovoltaic element comprising a silicon-based semiconductor layer having at least one pin junction on a support, wherein at least one i-type semiconductor layer comprises the silicon-based film as set forth in any one of claims 1 to
 5. 7. The photovoltaic element according to claim 6, wherein the silicon-based semiconductor layer is formed on a substrate comprising at least a first transparent conductive layer stacked on the support, and the first transparent conductive layer has the surface shape represented by the function f.
 8. The photovoltaic element according to claim 6, wherein the support is a conductive support. 